The present invention relates to an apparatus for and method of detecting the position of a pattern formed on a photosensitive substrate used in a lithographic process for manufacturing semiconductor devices, liquid crystal display devices and the like, and more particularly relates to a position detection apparatus for and method of measuring the relative position between patterns.
In photolithographic processes for manufacturing semiconductor devices, a pattern formed on a first object such as a mask or reticle is successively exposed through a projection optical system onto a second object, such as a substrate (e.g., a wafer) coated with a photosensitive material like photoresist. If there is a positional deviation between the resist pattern formed on the photosensitive substrate by exposure and a pattern already formed on the substrate by a previous process, problems arise such as a drop in the performance of the semiconductor device or a drop in manufacturing yield. Therefore, it is important to be able to measure the deviation in positions between such patterns.
An example of a prior art apparatus that measures the amount of positional deviation (i.e., the relative position) between patterns formed on a photosensitive substrate is disclosed in Japanese Patent Application No. Hei 8-273227. The prior art measurement apparatus disclosed therein uses an imaging optical system to detect the image of a resist pattern and the image of a predetermined pattern (circuit pattern) previously formed on substrate by a projection exposure process. The apparatus calculates the dimension (i.e., distance) between the patterns, namely the relative position, based on the resist pattern image and the pattern image formed (exposed) by the previous process.
However, the imaging optical system of the measurement apparatus in the prior art discussed above has optical members and the like such as lenses and glass plates. These optical members have fabrication errors, such as roughness in the ground surface, that arise during the optical member manufacturing process. Unfortunately, such errors affect the imaging characteristics of the apparatus. In particular, distortion is generated, which causes the position at which the pattern is imaged to be shifted from its ideal imaging position. Here, the ideal imaging position is that associated with a distortion-free imaging system. Thus, distortion arising from fabrication errors reduces the pattern position detection accuracy. To deal with the dramatic increase in recent years in the storage capacity of DRAMs, high-precision pattern position detection and high-precision measurement of the amount of pattern positional deviation are becoming more and more critical. Consequently, a reduction in the pattern position detection accuracy caused by fabrication errors in the measurement optical system can no longer be ignored.
In exposing a reticle pattern onto a wafer, the reticle and wafer need to be aligned so that the exposure levels are properly registered. One alignment method is the so-called FIA (Field Image Alignment) method. In the FIA method, an alignment mark provided on the wafer is illuminated perpendicularly by light having a broad wavelength band. The reflected light or diffracted light from the mark is converged and imaged onto a detector, such as a CCD image pickup surface by an imaging optical system. The position of the alignment mark is detected based on the detector signal. Then, alignment of the reticle and wafer is effected based on the position detection information of the alignment mark.
Even in exposure apparatus for semiconductors and the like, if residual fabrication errors are present in the optical members, detection errors will arise if the measurement position of the alignment mark changes due to the effect of distortion. This also leads to difficulties in accurately aligning the reticle and the wafer.
As described above, errors in the manufacture of an imaging optical system are caused by errors in the manufacture of the optical members, off-center errors such as errors in the assembly of the imaging optical system, as well as errors in the design of the imaging optical system. These all lead to the problem of reduced detection accuracy and ultimately, to errors in the position measurement of the patterns.
The present invention relates to an apparatus for and method of detecting the position of a pattern formed on a photosensitive substrate used in a lithographic process for manufacturing semiconductor devices, liquid crystal display devices and the like, and more particularly relates to a position detection apparatus for and method of measuring the relative position between patterns.
The present invention takes the aforementioned problems into consideration, and has the goal of providing an apparatus that can detect the position of a pattern with high precision by premeasuring information on the aberrations of the apparatus, and correcting the detected pattern position.
Accordingly a first aspect of the invention is a position detection apparatus for measuring the relative position of a pattern on a substrate. The apparatus comprises an illumination system capable of illuminating the pattern, and an imaging optical system arranged to converge light from the substrate and form an image of the pattern. The apparatus further comprises a detector that detects the image and generates a first output signal containing a representation of the image, and a position detection system, electrically connected to the detector, which detects a position of the pattern based on the first output signal, determines a deviation of the position from an ideal position, and generates a second output signal containing deviation information representing the deviation. Also included is a memory unit, electrically connected to the position detection system, that stores the deviation information contained in the second output signal. The apparatus also comprises a correction process unit, electrically connected to the memory unit, that generates a correction value for eliminating the deviation based on the deviation information.
A second aspect of the invention is a position detection method for detecting the position of a first predetermined pattern formed on a first object. The method comprises the steps of first, photoelectrically detecting a first image of the predetermined first pattern formed on the first object, then determining a positional of the first predetermined pattern based on the position of said first image in a detection field, then photoelectrically detecting a second image of a predetermined second pattern formed on a second object, then determining a position of the second predetermined pattern based on the position of second image on the second object, and then finally determining a positional deviation between the first and second images.